Assembled but have not been hit with a smoothing plane yet. Pretty good fit    

Planing it to smooth it out a bit

All smoothed

Prep is important. Even though this is practice in scrap, the pieces need to be perfectly flat and square. If it isn't taking the extra time to get it there will pay off. This is some scrap butternut that is a tad over 3" wide.    

I then label the boards and mark them out. These boards are identical thickness, but if not you want to lay out the thickness of one board on the other. A marking gauge is my preferred and recommended method. If you search through my other articles here I demonstrated making this one. 
This is the "Tail" board. Notice I mark it all the way around

The pin board is also marked, but only on the wide faces, not the edges

I'm going to demonstrate laying out the dovetails tails first. The tail board is cut straight across the top and angled down the face. I put the tail board in my vise and use a ruler, my 14 degree dovetail marker, a divider or compass and a marking knife    

I start by laying out the sockets for the half pins. I like to mark off 1/8" from the edge. I do so on each side and then transfer the angle down the face. The angle goes toward the center of the board. I then do the same for the other face. Again the angle goes toward the center of the board

I want 3 tails. I guess and set my compass to 1/3 the width between the marks on the board. I then "walk" the dividers across the board. I make adjustments until I can mark 2 points between the half pins - then mark them

Megan Fitzpatrick from Popular Woodworking has a much better way to do this

From those marks I use the ruler and mark 1/16" on either side leaving a 1/8" wide pin. I use my marker to transfer the lines down the face. I then knife the pencil lines along the top.

I choose not to knife the the lines down the face. That's because it's critical I am straight across, but not critical that I follow the exact angle. whatever angle these end up as will be transferred to the pin board.  My goal is to have the joint fit "off the saw". I don't like to chisel to knife lines after sawing. 

Choose your weapon and wax it. Find a saw you are comfortable with. For me it's the Gyokucho #311. The wax helps the plate slide easily and not bind

Get to sawing. Again, it's very critical the cut is square. Less critical (at this step) that the exact angle is followed. Take your time. Especially when you get close to the baseline. I like to make sure the "show side" is facing me

Saw out the waste. Some people advocate chiseling it, I highly recommend sawing the bulk of it. Here I am using the Gramercy tools turning saw, but any coping saw or fret saw will do

The kerf of this Japanese saw is too small to drop the blade into, so I saw from each side; corner to corner

Done with the saw. I left a bit of material. I do not want to saw into my baseline

Before I remove the waste I reinforce the scribed line with a knife only on the parts to be removed. 

I saw off the socket for the half pin. Using a wide chisel, I establish a ledge for the saw to ride in

I use a different saw for this operation. This is a cross cut and I like a more cross cut specific saw. I saw the corner first to establish straight and plumb, then finish the rest. I am very careful not to saw into the dovetail

The result. You can see the benefit of the deep scoring with the knife. Now I have a very clear picture of the baseline I need to clean up

I clean up the cut with a sharp wide chisel

Now it's time to clean up the baseline. I use a bench hook and a hold fast to keep it down to the bench. I also have a strop handy. The sharper my chisel is, the more accurate and crisp this will be. The chisel cannot be too sharp here, so I strop often

I start by relieving some material in front of the baseline so I have a ledge to chisel into

I don't drop my chisel into the knife line yet. A chisel is a wedge. Driving it down also drives it backward. I pare the waste back first    

You can see the result of that operation here. I carefully go all the way down - not stopping halfway yet

Now I drop my chisel in the baseline and chisel halfway down. Keeping the chisel dead straight. 

Once done I flip the piece and do the same from the other side. Be very careful here. Going past the baseline will result in gappy dovetails 

Completed the chiseling

Now I put the piece vertically in the vise and make sure the baselines do not have a crown in the middle. These do. I use the chisel to clean them up a bit, and make sure the corners are clean

Now I need to transfer the tails to the pins. On the pin board, the angled portion goes across the end grain and straight up and down on the face. I have the pin board in the vise with the tail board on top of it. I make sure the baseline of tail board lines up with the edge of the pin board, then carefully mark the board with a knife

There is the result. I deepen the knife lines a bit and then penciled them in so they show better in pictures. I don't normally pencil them in. Cutting these perfectly is the most critical part of the process. 

I use my marker to transfer the vertical lines down the face. Remember that I may not have cut to the exact angle on the tail board. That is okay, but I will not use the marker to transfer or reinforce the knife lines on the top. They may be "off", but it won't matter    

I marked out the waste. It's very important to cut into the waste side. Another reason I like the Japanese saw is the kerf is so thin I can split my knife line and have a perfect fit as long as I saw very carefully and very accurately

The pin board is sawn

I remove the waste in a similar manner with my turning saw, staying clear of the baselines. I will remove the rest of the waste with a chisel

Here I what the piece looks like after I saw the bulk of the waste. At this point I like to test the fit. 

Perfect fit, right off the saw. This is my goal. They don't go all the way down because I have to chisel the waste still, but as long as I am careful in the next step, I'm home free

Chiseling here requires some awareness of where your edge is. You can see the socket is tapered. It's wider at the top than the bottom. I want the wider side up.

Because it's narrower at the bottom, I choose a chisel that clears the narrowest point. I remove the waste like with the tails. Starting from the edge and working back toward the baseline. Only this time I have to keep clear of the taper and stay to the center

I like to angle the chisel slightly under 90 degrees and chisel all the way though. I learned this from an excellent craftsman named Israel Martin Benito. His blog (Spanish language) can be found here. It's not conventional, but try it at least once. It works well    

Here is how I remove the waste from the edges. Very carefully, and slightly under 90 degrees so I don't accidentally go past my baseline on the other side 

Here is the other side. There is very little left here. Just a single tap with a chisel cleans it up

Like with the tails, I do a final check and clean up vertically in the vise. Then the moment of truth

Perfect fit. Just a tad proud, but a sharp hand plane can fix that. Paring the pins or tails to knife lines with chisels is very error prone for me and never works out. This is why I prefer to saw dovetails and not carve them.

The other side. Also a perfect fit, no paring.

The corner came out well

And it's dead square

After planing it's ready for some finish. No sawdust and glue, no wedges needed. It's just muscle memory and practice (repetition)